Separating elemental phosphorus from impurities



Nov. 8, y1938. 1 H. ALMND SEPARATING ELEMENTAL PHOSPHRUS FROM IMPURITIESFiled Aug. 17, 1937 Law/ence H A/mono INVENTOR BY MLB-w ATTORNEYPatented Nov. 8, 1938 grasas PATENT OFFI'QE SEPARATING ELEMENTALPHOSIHOR'US4 FROM IMPURITIES Lawrence H. Almond, Nash-ville, Tenn..Application August 17, 1937, Serial No. 159,537

3 Claims.

(Granted under the actl of March 3, 1883, as amended April 30, 1928;3,700. G. 757) 'I'hisapplicationis madeunder the act of March 3, 1883,as amended by thev act of April 30, 1928,

and. the invention herein described, if patented,

may be manufactured and usedby or for the Government for governmentalpurposes Without they payment to me of any royalty thereon.

This inventionl relates'to a process of and apparatus for the separationof elemental phosphorus from crude elemental phosphorus, particularlymixtures of elemental phosphorus. and solid impurities.

One, of the objectsof this invention is tosepa- `rate elementalphosphorus from mixtures containing the same without converting theelementalphosphorusinto phosphoruspentoxide or other phosphoruscompounds. Another object of this invention is to separate elementalphosphorus from mixtures containing the same in the form of yellow orwhite phosphorus Without converting-this phosphorus intoredphosphorus.Other objects of this invention include the provision of a process andapparatus for the continuous and economical separation of elementalphosphorus from mixtures of the same carrying solid impurities..

In the production of elemental phosphorus by the reduction of phosphaticmaterial in a phosphatereduction furnace, whether it be a blast furnaceor an electric furnace, there is always produced'in the process acertain portion of elemental phosphorus associated with ne particles ofmaterial carried over from the phosphate reduction furnace with the gaswhich presents serious diiiiculties both from the standpoint ofl theloss of elemental phosphorus as far as its Ydirect recovery is concernedand the disposal of this material, since the presence of elementalphosphorus therein: makes it extremely hazardous. A substantially drymixture of elemental phosphorus and solid impurities may be obtainedyeither during the separation of dust from the phosphate reductionfurnace gas or by the indirect condensation of elemental phosphoruscontained in such gas While a mixture carrying a considerable proportionof Water is obtained when the elemental phosphorus in a phosphatereduction furnace gas is condensed. by a direct condensation with acooling liquid, such as water. Such mixtures, usually called sludge, mayusually contain' an average of- 50% of elemental phosphorus by weightalthough the actual amount may vary from a few percent to considerablyhigher than this value.

ity has been proposed to separate the elemental phosphorus from suchsludges by burning the elemental phosphorus therefrom in a rotary kilnwith or without the presence of other materials, such as rock phosphate.This elemental phosphorus under such. circumstances is converted tophosphorus pentoxideor other phosphorus compound: depending upon theconditions under 5 Which the separation takes place. It has also beenproposed to distill the elementalphosphorus from such sludges containingthe same. This has only been accomplished in a discontinuous mannerwhich, inadditionto not only being expensive, is extremely slow and forthe latter reason causes the conversion of. av substantial proportion ofthe white or yellow phosphorus into red phosphorus which is ordinarilyundesirable.

I have discovered a process for separating elemental phosphorus, fromsludges containing the same by continuously feeding the sludge to anenclosed ilash distillation zone, by flash distilling continuously thephosphorus and water in the sludge admitted to the zone, by separatingthe vaporized phosphorus and water from the solid impurities carried bythe sludge and by withdrawing the solid impurities from the enclosed ashdistillation zone continuously. I have also discovered ank apparatus foreilectively carrying out this process which is entirely enclosed so thatthere is no conversion of the elemental phosphorus into phosphoruspentoxide or other phosphorus compounds.

In the accompanying drawing, which forms a part of the specification andwherein reference symbols refer to like parts wherever they occur,

Fig. lis a diagrammatic plan View of one form of apparatus forV theembodiment of my invention, and

Fig. 2 is a diagrammatic, vertical, sectional view of the apparatusshown in Fig. l..

InA Fig. 1 and Fig.` 2, a mixture containing elemental phosphorus, solidimpurities and water from a storage tank (not shown) is deliveredthrough line I, into steam jacketed feed tank 3. The mixture in thebottom of feed tank 3, is moved upwardly from the troughed bottom offeed tank 3, by means of variable speed drive screw conveyer 5, enclosedexternal to feed tank 3, by shell l. The mixture delivered to the upperend of screw conveyer 5, passed through line 9, into the lower end ofshell II, enclosing a second variable speed drive screw conveyer I3,with shell I I, located in furnace I5, equipped with burner Il, andstack I9. IIhe interior of furnace I5, is maintained at a temperaturesuflicient to maintain the distillation Zone within the shell II, at atemperature suiiicient to cause a rapid vaporization ofthe elementalphosphorus and the water 55 di, into steam jacketed make-up tank 43.

in the mixture delivered into shell I I, and at least at such a ratethat both of these materials will be substantially completely vaporizedby the time the solid impurities have been conveyed to the upper end ofshell I I, by screw conveyer I3. The vaporized elemental phosphorus andWater pass from the upper end of shell II, into separator 2l, whereinsolid particles carried by the gas stream may fall out due to thereduction of gas velocity obtained in separator 2 I. The vaporizedelemental phosphorus and Water pass from separator 2 I through vaporline 23, into indirect condenser 25, maintained at a temperature notlower than the melting point of elemental phosphorus. The condensedelemental phosphorus and Water pass fromV condenser 25, through line 21,into receiver 29, jacketed with hot water to maintain the elementalphosphorus in the bottom of the receiver mol-` ten. The moltenphosphorus in the bottom of receiver 29, is withdrawn through valve line3 I, to storage. The solid impurities moved by the screw conveyer I3, tothe upper end of shell II, pass through line 33, which is Water sealedinto receiver 35. -The solid impurities delivered to receiver 35, areintermingled with water, either the condenser water from condenser 25,or a separate water supply, and the mixture is withdrawn continuously ordiscontinuously through valve line 3l. The water separated in receiver29, passes through line 39, and any water separating to the top of feedtank 3, kpasses through overflow line This Water which always carries atrace of elemental phosphorus passes through valve line 45, into pump41, from which it is delivered to the storage tank (not shown) whichalso serves as a sludge mixing tank.

It is evident that there are numerous factors Awhich will influenceconditions for the most satisfactory operation of my invention, theactual limits of which cannot be established except by a detailed studyof each set of raw materials and finished products involved.

The original sludge may be either a mixture of elemental phosphorus,phosphorus and solid impurities or a mixture of elemental phosphorus,solid impurities and water. When the original material is asubstantially dry mixture of elemental phosphorus and solid impurities,it is necessary to add water to this mixture, in an amount at leastsufficient to form a semi-fluid mixture which is to'besupplied as thefeed material.V Likewise -if the water content of such a wet mixture islow it is necessary to add additional water.

The feed is advanced positively through a distillation zone heated insuch a `manner that the elemental phosphorus and water contained thereinis flash distilled or at least rapidly vaporized and all so vaporized bythe time the solid impurities have passed through the distillation Zone.This movement of the feed may be conveniently accomplishednby a screwconveyer, although any other positive means for effecting the same orequivalent results are equally vsuitable. It has been found desirable incertain instances to charge the feed material to the screw conveyerpassing through the furnace by means of another screw conveyer feedingdirectly from the bottom of the feedtank in sucha manner that a partialadjustment of the water content of the feed and a more regular chargingof the feed is obtained with the discharge from this conveyer feedingintoV the conveyer passing through the distillation zone. In any event,the respective conveying means should have a variable speed in orderthat adequate adjustment Vmay be madeV according to the variations inthe composition of the feed and the circumstances under which theseparation of the elemental phosphorus and water from the mixture arecarried out.

The enclosed distillation zone may be heated by locating it within asuitable designed furnace, either fuel red or electrically heated. Thetemperature Within the distillation zone should ordinarily be maintainedat 750 to 800 F.

The vaporized elemental phosphorus and the- Yzone toaccomplishsubstantially the same result.

In some instances, it may be more desirable to have the screw conveyerin the distillation Zone` flt in more closely with its shell and`provide a separator for accomplishing the separation of traces of solidimpurities carried by the vaporized material.

The vaporized; phosphorus andwater are conv densed and the constituentsof the condensate separated.

The solid impurities which remain on passing the feed through thedistillation Zone are discharged into a receiver, mixed with water toVform a sludge and disposed as such. The entire process is carried out inan enclosed apparatus to prevent oxidation of the elemental phosphorus.It will be noted from the drawing that the feed device is sealed fromthe atmosphere and that the outlet carrying residue of solid impuritiesis also sealed against the admission of `atmospheric oxygen.

Water which has been in contact with elemental phosphorus usuallycarries traces of the ,A

later and must be handled with care. In this instance, water separatingfrom the feed in the feed tank and water condensed along with vtheelemental phosphorus is runk to a make-up tank and used as a source ofwater for admixing with the sludge as required. Some of this water may,

however, have to be withdrawn from the system as the circumstancesrequire. Y

The residual solid impurities may be removed from the receivercontinuously or discontinuously, either by direct application of a waterjet or by continuous passage of aV flow of water through the receiver,such as may be available as the condenser water discharged from thecondenser used to condense the vaporized elemental phosphorus and Water.y

It will be seen, therefore, 'thatV this invention actually may becarried out by the modification of certain details withoutdeparting fromits spiritor scope. v Y

I claim:

l. Process of separating elemental phosphorus from a mass of elementalphosphorus and solid impurities, such as obtained by separating dustfrom phosphate reduction furnace gas or by indirect condensation ofphosphorus from phosphate reduction furnace gas, which comprises, mixingat least a sufcient quantity of water with the mass to form a semi-Huidmixture; feeding the mixture continuously into an enclosedV flashdistillation zone maintained at approximately 750 to 800 F.; flashdistilling the phosphorus and water in the mixture continuously;separating the vaporized phosphorus and Water from the solid impuritiescontinuously; condensing the phosphorus and Water; and withdrawing thesolid impurities from the enclosed flash distillation zone continuously.

2. Process of separating elemental phosphorusl from a mixture ofelemental phosphorus, solid impurities and Water, such as obtained bythe direct condensation of phosphorus from phosphate reduction furnacegas, which comprises, adjusting the Water content of the mixture untilit is semi-uid; feeding the mixture continuously into an enclosed flashdistillation zone maintained at approximately 750 to 800 F.; hashdistilling the phosphorus and Water in the mixture continuously;separating the vaporized phosphorus and Water from the solid impuritiescontinuously; and withdrawing the solid impurities from the enclosedflash distillation zone continuously.

3. In the process of separating elemental phosphorus from a mixturecomprising elemental phosphorus, solid impurities and Water, the stepsWhich comprise, adjusting the Water content of the mixture until it issemi-fluid; ash distilling the phosphorus and Water continuously in anenclosed flash distillation zone maintained at least at a temperaturesuiciently high to flash distill the phosphorus and water in the mixtureadmitted to the Zone; separating the Vaporized phosphorus and Water fromthe solid impurities continuously; and withdrawing the solid impuritiesfrom the enclosed ilash distillation zone continuously.

LAWRENCE H. ALMOND.

